.shadow(@scrollbar-shadow-size; @placement) {
    position: absolute;
    z-index: 1;
    display: block;
    content: '';
}

.shadow(@scrollbar-shadow-size; @placement) when (@placement = 'top') {
    top: -@scrollbar-shadow-size;
    left: 0;
    width: 100%;
    height: @scrollbar-shadow-size;
    box-shadow: 0 1px var(--f-shadow-radius-sm) var(--f-shadow-color-sm);
}

.shadow(@scrollbar-shadow-size; @placement) when (@placement = 'bottom') {
    bottom: -@scrollbar-shadow-size;
    left: 0;
    width: 100%;
    height: @scrollbar-shadow-size;
    box-shadow: 0 -1px var(--f-shadow-radius-sm) var(--f-shadow-color-sm);
}

.shadow(@scrollbar-shadow-size; @placement) when (@placement = 'left') {
    top: 0;
    left: -@scrollbar-shadow-size;
    width: @scrollbar-shadow-size;
    height: 100%;
    box-shadow: 1px 0 var(--f-shadow-radius-sm) var(--f-shadow-color-sm);
}

.shadow(@scrollbar-shadow-size; @placement) when (@placement = 'right') {
    top: 0;
    right: -@scrollbar-shadow-size;
    width: @scrollbar-shadow-size;
    height: 100%;
    box-shadow: -1px 0 var(--f-shadow-radius-sm) var(--f-shadow-color-sm);
}